Basically, the assumption there is that the current equilibrium is optimal or close to optimal. The problem is that this is often untrue. If I'm being inefficient, there is no reason for an improvement not to be completely free, after all.

It also smacks of "conventional wisdom" which is often much more conventional than wise.

More pertinently, I think this can apply to evolution. Now, clearly, I am no expert on evolution, so I could be completely off-base. But my understanding is that evolution can get caught in local maxima. That is, there could be some sufficiently remote global maximum in the fitness function that isn't reached because any probable mutation hits a lower value between the current state and this possible maximum.

I suppose an example could be about how evolution never came up with the wheel. I think there are cases where wheels would increase fitness, but they are simply too remote from existing organisms to reasonably evolve.

If such an effect exists, then some sort of design process could overcome it. In this case, we could strictly improve on evolution. Now, I'm not sure if this is an actual effect, but it seems plausible. If anyone has any actual studies on the subject, I would like to see them.